Hydroforming is well known for its ability to form an integral hollow beam with a complex shape, something which would otherwise have to be fabricated from several pieces and/or bent to shape. Typically, a round tubular blank is inserted between a pair of dies which have an internal cavity in the form of the desired exterior shape of the final part. Then the ends of the tube are plugged and the interior chamber of the tubular blank is pressurized, generally with water or hydraulic fluid, to force it into the shape of the die cavity. The completed part is then de-pressurized and removed.
The hydroformed part often, in its final application, requires that one or more articles be attached to it. For example, hydroformed components are used in making subframe assemblies in automobiles, such as shown in FIG. 1. The subframe assembly A often have metal stampings S and cross-member C welded thereto to form the subframe assembly and permit the subframe assembly to be fastened to a frame assembly. To accomplish this, typically once the tube T has been hydroformed, it is removed from the die and placed in a welding jig, along with metal stampings S, so that a welding machine can weld stampings S to tube T to yield hydroformed assembly A. However, these additional fitting and welding steps add process cost and time, and also have a tendency to introduce errors such as additional dimensional variation or missed process steps, both of which can be detrimental to the function and economics of the part.
Referring to U.S. Pat. No. 5,845,382 to Schultz et al., it is known in the manufacturing of a seat frame assembly to position a hollow cylindrical part in a die and circumferentially around a tube to be hydroformed prior to hydroforming, and then hydroforming the tube to expand it outwardly to integrally engage the outer cylindrical to effectively lock the pieces together. While this technique does limit the requirement for additional assembly and welding steps, its application is limited to situations where the article to be circumferentially attached surrounds the hydroformed part.
Accordingly, there is a need for an improved method and apparatus for attaching an article to a hydroformed tube which can decrease process costs and time, as well as increase the accuracy and repeatability with which mass produced parts are fabricated.